Power is a recharging attribute in Empire Earth assigned to units or buildings with special abilities. Units such as Priests, Prophets, Strategist Heroes, and certain cybers all have a power bar, and the abilities require specific amounts of power.
Power will recharge slowly overtime. Players can spend resources on technology upgrades to increase power regeneration -- usually for Priests and Prophets. Power can also be increased in capacity with cybers by simply upgrading it, like any other attribute.
Power appears over a units head in the world, in the user interface (UI) in the bottom left when that unit is selected.